Microelectromechanical systems (MEMS) are small devices made of electrical and mechanical components, designed to work together to sense physical properties in their local environment. For instance, MEMS pressure sensors are designed to sense and report the pressure of a fluid or environment in which the pressure sensor resides.
MEMS pressure sensors may be piezoresistive devices, which make use of changes in the resistivity of a semiconductor material when subjected to mechanical stresses. A piezoresistive sensor operates based on a diaphragm structure which deflects in response to applied pressure. However, the diaphragm structure will also deform from other stressors: for instance, it may deform from thermal stresses associated with stacks of different materials that have varying coefficients of thermal expansion. Alternatively, the diaphragm structure may deflect from stresses associated with mechanical mounting used to secure the diaphragm on a larger package.
Stress isolation in piezoresistive sensors is crucial to both function and longevity. Accuracy of a sensor, particularly in high temperature environments, is much improved when temperature stress is reduced. In the prior art, stress isolation has been addressed through traditional stress isolation stacks with glass pedestals, or inline stress isolation stacks as described in U.S. Pat. No. 9,010,190. Both methods found in prior art sensors utilize larger areas to accomplish stress isolation, give low yielded signals, and are costly.